1. Technical Field
The present invention relates to a non-aqueous electrolyte solution for a lithium secondary battery, and a lithium secondary battery having the same. More particularly, the present invention relates to a non-aqueous electrolyte with excellent cycle performance and overcharging stability, and a lithium secondary battery having the same.
2. Background Art
With recent and rapid developments of information communication industries, electronic devices have become smaller, lighter, slimmer and more portable. As a result, a demand for batteries having higher energy density as a driving power source of an electronic device is increased. Among such batteries, lithium secondary batteries satisfy this demand, and numerous studies towards improvements are now in progress actively. A lithium secondary battery includes a cathode, an anode, an electrolyte and a separator that provides a passage for lithium ions moving between the cathode and the anode. When lithium ions are intercalated into or disintercalated from the cathode or the anode, the lithium ion secondary batteries generate electric energy by means of a redox reaction.
A non-aqueous electrolyte used for lithium secondary batteries generally includes an electrolyte solvent and an electrolyte salt. However, the electrolyte solvent is decomposed on an electrode surface or co-intercalated between carbonaceous anode layers while a battery is charged or discharged, thereby collapsing the anode structure. It may damage stability of the battery.
It is known that such problems may be solved by means of a SEI (Solid Electrolyte Interface) film formed on a surface of an anode by means of reduction of the electrolyte solvent when a battery is initially charged. However, the SEI film generally insufficiently serves as a film for continuously protecting the anode, and its life and performance are deteriorated as the battery repeats charging/discharging. In particular, a conventional SEI film for a lithium secondary battery is thermally unstable. Thus, in case a battery is operated or left alone under a high temperature, the SEI film may be easily collapsed due to electrochemical energy and thermal energy increased as time goes. Thus, the battery performance is more deteriorated under a high temperature. In particular, gas such as CO2 is continuously generated due to collapse of the SEI film and decomposition of the electrolyte, which increases inner pressure and thickness of the battery.
In addition, cyclohexylbenzene and biphenyl were frequently used as an overcharging inhibitor. However, cyclohexylbenzene and biphenyl become factors of decreasing battery capacity and deteriorating normal temperature performance though it prevents overcharging.
In order to solve the above problems, Japanese Laid-open Patent Publication No. 1996-45545 discloses a method of using vinylene carbonate (VC) as an electrolyte additive for forming a SEI film on a surface of an anode. However, VC is easily decomposed to generate gas at a cathode on the condition of high temperature cycle or high temperature preservation, which deteriorates performance and stability of a battery.
Also, Japanese Laid-open Patent Publication No. 2002-329528 suggests controlling gas generation at a high temperature by using an unsaturated sultone compound. In addition, Japanese Laid-open Patent Publication No. 2001-006729 suggests improving high temperature preservation characteristics by using a carbonate-based compound including a vinyl group. However, these methods does not ensure a firm SEI film, so the conventional problems still remain unsolved.